The present invention relates to a scanning apparatus for use in exposing the photoconductive drum in an electrophotographic copying machine, and more particularly to optical scanning apparatus and method utilizing holographic techniques.
The present invention is especially suitable for use in a typical electrophotographic copying apparatus which is presently used in industry. This typical apparatus includes a rotatable drum having a photosensitive outer circumferential surface, and means for rotating the drum in a controlled fashion so that its outer surface defines a fixed annular path of movement. The apparatus produces copies by first forming an electrostatic image corresponding to the particular information to be copied on the photosensitive outer circumferential surface of the drum. Thereafter, the latent image is developed by means of toner particles, specifically electrically charged heat fusible particles, which are applied to the image bearing surface in a specific way. Finally, the applied toner particles are transferred from the drum to the blank sheet and thereafter fused thereon for transforming the sheet into a permanent copy. After the toner transfer is complete the drum is cleaned so that no trace of the electrical image either as represented by toner particles or static electric charge remains.
It is an objective of the present invention to provide an improved means for exposing the photosensitive outer surface of the drum to the information to be copied.
It is a further objective of the present invention to provide a means for conveying the high speed output of a computer or the like to the photosensitive surface of the recording drum.
Multibeam optical scanning systems capable scanning plural lines at a time have previously been proposed as a high speed output device for a computer or the like.
One example of such a multibeam optical scanning system is shown in U.S. Pat. No. 4,348,080. In this system illustrated by FIG. 1 herein a conventional laser recording apparatus is shown including a laser light source 1; a beam expander 2; a convergent lens 3; and an acoustooptic device 4 which modulates the laser light source by the incoming information from a computer or the like on line 4A. The multifrequency output passes through magnification adjustment lens 5, cylindrical lens 6, and is then rotated across the surface of the drum by rotating polyhedral mirror 7 through lens 8 and cylindrical lens 9. Similar acoustooptic devices are shown in U.S. Pat. Nos. 4,312,588; 4,390,235; and 4,344,677. All such devices however are quite expensive since they must have a very wide band width.
U.S. Pat. No. 4,348,080, as illustrated in FIG. 2 herein referred to above, is an effort to improve on these prior art device by the use of a rotating disc 14 carrying a plurality of holograms. This rotating disc is used in place of the rotary polyhedral mirror 7 of the prior art. However, the acoustooptic device drive insert which is shown in FIG. 2 of that patent remains complex and costly.